The invention relates to an electronic device, and more particularly, to an image sensor device.
CMOS image sensor devices are used in a wide variety of, applications, such as digital still camera (DSC) applications. These devices utilize an array of active pixels or image sensor cells, comprising photodiode elements, to collect photo energy for conversion of images to streams of digital data.
FIG. 1 is a cross section of a typical image sensor device. In FIG. 1, a typical image sensor device 100 is illustrated in cross section, comprising a semiconductor substrate 101 having an array of photodiodes 120 therein. Each photodiode 120 comprises, for example, an n-type region 124 in a p-type region 122. Each photodiode 120 is separated from other photodiodes by an array of isolation structures 110, such as shallow trench isolation (STI). Thus, an array of pixels is obtained. The pixels convert incoming light 160 from a light/image source to electrical signals via the photodiodes 124. The substrate 101 is covered by a series of dielectric layers 130, such as an interlevel dielectric (ILD) layer and intermetal dielectric (IMD) layers. A color filter layer 140 overlying the substrate 101 comprises red regions 140a, green regions 140b and blue regions 140c. 
FIG. 2 illustrates curves of wavelength versus transmittance of three major colors. In FIG. 2, the blue curve presents extremely low transmittance at a wavelength of about 580 Å˜650 Å. Exposure apparatuses, such as steppers, typically use light with wavelength of 633 Å for alignment. Consequently, extremely low transmittance of the blue photoresist of the color filter is likely to cause alignment failure.